Preparation of petroleum pitch



' to degrade any cutter oil to fuel oil.

United PREPARATION F PETROLEUM BITCH Harold'euther, Penn Township,Allegheny County, and

Applicationnluly 2, 1953, Serial No. 365,582

. 2 IClaims. (Cl.196-76) This invention relates to a petroleum pitch,and more `particularly to asolidl -petroleum pitch Iand a process forlits preparation from asphaltic or naphthenic'cr'udes.

l In a conventional'process for the reiiningof petroleumcrudes,?ftherude is fractionatedinan atmospheric dis- -tillation-towerto separate -thedistillates from the heavy ynonevolatile residue. 1a'visbreaking operation in which itis'thermally cracked at rnildcrackingconditions -toy reduce its viscosity.' Ga-s l.oil or other distillatesproduced inthe visbreakingop- `-eration arethen ordinarily recycledthrough othercrackingvoperations at increased` severity toproducegasoline having improved anti-knock and other-characteristics L l:Thevisbroken bottomsV are blended with a-relatively light oil, for examplea-virgin distillate or a cycle stock from azcrackingprocess, designatedas acutter oil, to yield I a. fuel oil,-ordinarily. identified as No. 6fuel oil, having van :acceptable-viscosity. Since insutlicient lightoil'to blend 'withf the bottoms and cut their viscosity to theTheresidue is then 'passed through desired range is produced in therefining of certain heavy crudes, it is sometimes necessary to obtaincutter oil from an outside source. The price of No. 6 `fuel oil i-sfrequently lowerithan the price ofthe crude, and isconsiderably lowerlthan the price of distillate: productssuch as domesticheating oils, -inwhich the light oils used as cutter oils ordinarily .are employed. Forthis reason, a process for refining petroleum crudes which. will resultin a minimum degradation of cutter oils to No. 6 vfuel oil` isdesirable.

YThe processes for the catalytic. crackingrof vgas oils havefrequentlycaused refiners rto alter .their refining processes bythe substitutionof vacuum distillation for .thermal cracking or other treatment of thebottoms from Ithe atmospheric distillation. ylnthis manner, the amountsof virgin stock for charging to catalytic cracking operations isincreased. However, the bottoms from the .vacuum reduction-are highlyviscous andmust'be blended with a cutter oi-l to produce a fuel oilhavinganacceptkable viscosity. The vacuum reduction, therefore, in-

creases .the amount of virgin catalytic cracking charge stock obtainedfrom the crude, but still has the disadvantage of requiring blending ofcycle stock withbottoms I. to form No.y 6 fuel oil.

One process that is used to reduce the amount of No. 6 fuel oil producedfrom a crude is the coking operation.

In that process, the bottoms from adistillationI tower or from othercracking processes are discharged from a cracking furnace into a cokingdrum in which `they Vare held for a suiiicientperiod of time to convertthe heavy material to coke. Ordinarily, no No. 6 tuel oil is produced ina coking operation; hence, it is not necessary However, the cokingoperation is expensive ,because of high labor and utility costsresulting from the diiiiculty in removing coke from the coking drum.

According to this invention, certain heavy asphaltic for naphtheniccrudes of low hydrogen to carbon ratio -are extremely deeply reduced ina continuous vacuum rates Patent1 2,796,388" Patented June 18, 1957flash-distillation. Theiresiduefrom the 'vacuum reduc- `tion is a'solidpetroleum'pitch having a very high softenvingpointmaking it suitable foruseas a solid fuel, or, l-in-some instances, as 'abinden By thevproductionof *the solid petroleum pitch in thismanner, the hydrogento-carb'on'ratio Aof'thedistillates isincreased by removal of a highproportion of the'carbon of the lcrude'oil in thepitch. In'addition',ans increased 'amount of virgin -idistillate ysuitablev'as a charges-tock for catalytic cracking petroleum pitches fof' 'this' invention.

I lReferring to the'ldrawings; the heavy crude feed passes throughLline'lOto aA pre-heater l2 in which it is heated 20` p. s..i.-vgauge.lIn'zthe usual operation, a gasoline v to a temperature sullicient tovolatilize a portion 'of the zdistillable fractions of the crude.

Pre-heater l2= may -be of anyi suitable typek such .as a heat exchangeror a tired heater. The heated crude is discharged from thepre- .fh-eaterflZvinto. an 'atmospheric distillation tower l14 in which :gases:and1:lowboiling fractions ofv thel crude are vaporized 'and'di-soharged-overhead through a line I16.. Typical ,conditions at .the inlet to thetower are atem- ;perature of-..iapproximately 700 F.v and `a pressure offraction will bewwlthdrawn through aside drawoff 18 and a-gas=oilthroughthe side-drawoff 20. Atmospheric distillation tower 14 may be-of anyconventional design and thedistillate Aproducts Withdrawnfrom the towerwill dependuprimarilyz'upon the design of'ithe tower; the-requirements-of the particular refinery, and :the vcharac- .terist-ics-of the feedstock.

The bottoms from atmospheric distillation tower 14 are withdrawn-through a-line 22 and passed through a heater 24 in which they areheated to a temperature suiciently-high to\permit an extremely deepvacuum ,reduction of the bottoms. .high-softening point petroleumpitches of this invention,

In the preparation 0f vthe the formation of-coke should be avoided;hence,v the maximum temperature in heater 24 will be limited by thecracking of the bottoms to form coke and will be dependentupon'the'characteristics of -the bottoms and the .heatingcurve of thefurnace 24. Ordinarily, the temperature-inheater 24 will range fromapproximately 650 F. to a maximum of approximately 850 F. Thetemperature actuallyl employed will be governed, in part, upon the rateat which the bottoms are passed through `the furnace, the pressureemployed in the vacuum distillation, and the lamount of steam addedtothe bottoms ,to aid in thev distillation.

The hot bottoms from heater 24 are passed through 1ine726into alcontinuous ilash vacuum distillation tower 28. Steam is preferablyadded to the bottoms, as through line 27, to reduce the vacuum requiredfor the distillation. The/temperature and pressure in tower 28 imust'besuch as to cause avery deep reduction rof the crudes to form thepetroleum pitch of this Ainvention as la residue. The minimumdistillation temperature that may be employed in tower 2S will depend inpart upon the particular crude being treated, and in general the heavierandmore naphthenic the crude, the lower the distillation temperaturerequired. yIn general, the distillation temperature in tower range 28,corrected to 760 millimeters of mercury will range from a minimum of1050 F. for very heavy crudes such as Baxterville crudes 4to a maximumin the range `of approximately 1200 F. Distillation temperatures higherthan 1200" F. might be employed if the heatingrcharacteristics of theheater 24, and other conditions, permitted heating to highertemperatures without -excessive coking.

The distillationtemperature in tower'28 is directly de- Y tower, a pitchhaving a softening point, determined by ASTM D36-26 ring and ball test,of 360 F. may be obtained by vacuum distillation in tower 28 at a flashtemperature of approximately 1070 F. (corrected to 760 millimeters ofmercury). On the other hand, if a pitch having a softening point of 472F. is desired, a temperature lof `approximately 1200 ^F. (corrected to760 millimeters of mercury) in the vacuum distillation tower isrequired.

It is necessary in the preparation of petroleum pitches to make anextremely deep cut into the heavy asphaltic crudes without substantialformation 'of coke. Continuous ash vaporization at high vacuum isparticularly suitable. Volatile components remaining in the reducedcrude, together with steam which is generally added, aid in thevaporization of extremely heavy oils in a continuous ash vacuumdistillation tower to facilitate their removal from the pitch Withoutemploying excessively high temperatures. Batch distillation processesare not satisfactory because of the very high temperatures required todistill the heavy oils, and the long periods at which the residue is ata high temperature.

A gas oil is withdrawn overhead from Vacuum distillation tower 28through line 30 and passed to a condenser 32. Non-condensable gas isWithdrawn from the system by a steam ejector or other vacuum pump 34 tomaintain a vacuum on the tower 28. The gas oil condensed in condenser 32is suitable for use as a furnace oil or catalytic cracking charge stock,`and is delivered from the system by a pump 36. The residue from thebottom of vacuum distillation tower 28 constitutes the novel petroleumpitch of this invention, and is withdrawn Ias a liquid through line 38by means of a pump 40 and delivered to any suitable cooling andsolidiiication equipment.

The petroleum pitches of this invention are characterized by a high butfinite softening point above 350 as determined by the ring and ball ASTMtest D36-26. The specific gravity of the pitch is in the range of 1.050to approximately 1.20 and in most instances in the range of 1.10 to1.20.

The petroleum pitches are brittle, dark and resemble gilsonite ratherthan petroleum coke in their characteristics. In addition to having anite softening point, the petroleum pitches are substantially completelysoluble in carbon disulfide, benzene, and trichloroethylene. Thepetroleum pitches contain less than 0.4% material insoluble in refinedcreosote solvents (Kolineum). 'The acetone insoluble materials in thepitches will range from approximately 80 to 95%, 4and the Conradsoncar-bon residue (ASTM test D189*46) is above about 40%. The petroleumpitches `of this invention have a low penetration ofthe order of aboutto 5 at 210 F./ 100 grams/5 seconds as determined in accordance withASTM test D5-49, and `are characterized by a susceptibility factor yofabout 15 to 25. The susceptibility factor may be calculated from thefollowing formula:

Penetration (a) 150/100 g./5 sec. L 114/200 g./5 sec. V

Penetration 185/ 50 g./5 sec.

@ 150/100 g./5 sec.)

Eastern Venezuela, Coastal, and California crude oils are also suitablefor the preparation of petroleum pitches by the method herein described.

Whether or not a crude oil is a satisfactory charge stock from whichhigh softening point pitches may be prepared according to this inventionmay be determined by the following test procedure. Furnace oil isdistilled from the crude oil Iand the bottoms from that distillation arecut at a 1030 F. flash temperature, corrected to 760 millimeters ofmercury absolute pressure, `and the asphaltene `content of the resultingAbottoms determined in accordance with the pentane precipitationtechnique of ASTM test D893-50T. The asphaltene content of the bottomsform a 1030 F. flash temperature of furnace loil-free crude oilssuitable for the preparation of pitches according to this invention isabove :about 30%.

Example 1 A Baxterville, Mississippi, crude having a gravity ofapproximately 15.3 API was reduced to 95.2% bottoms in an atmosphericdistillation. The bottoms were then vacuum reduced in a continuous flashdistillation at a flash temperature of approximately 700 and an absolutepressure of 41/2 millimeters of mercury. Steam was added to the reducedcrude at the rate of 26.1 pounds per barrel of charge. The flashtemperature, corrected to 760 millimeters of mercury, was l068 F. Thedistillate taken overhead from the vacuum distillation constitutedapproximately 69.4% of the crude by Volume and had a gravity of 22.4API. The petroleum pitch from the vacuum distillation uponsolidification had a specific gravity of 1.099 and a softening point, bythe ring and ba'l'l test, ASTM D36-26, of 360 F. The penetration of thepitch at 210 F./ 100 grams/5 seconds was 4. The Conradson carbon residueof the pitch was 431/2% and the percent of the pitch insoluble intrichloroethylene was 0.08.

Example 2 The reduced crude from the atmospheric distillation describedin Example l was vacuum distilled at a flash temperature of 775 F., aash pressure of 5.9 millimeters of mercury, and a steam addition rate of28.1 pounds per barrel of charge. The flash temperature, corrected to760 millimeters of mercury, was l160 F. The pitch recovered as bottomsfrom the vacuum distillation constituted 20.8% of the crude by volumeand had a softening point by the ring and barl'l test method of 390 F.The Conradson carbon residue of the pitch was 481/2 percent and thepercent of the pitch insoluble in trichloroethylene was 0.11. Thepenetration of the pitch at 210 F./ grams/5 seconds by ASTM test D5-49was 0.

Example 3 The reduced crude from the atmospheric distillation describedin Example l was ashed at a temperature of 799 F., a pressure of 7.4millimeters of mercury, and a steam addition rate of 31.8 pounds perbarrel of charge. The ash temperature, corrected to 760 millimeters ofmercury, was 1201 F. The pitch recovered as bottoms from the vacuumdistillation constituted 1.7.9 percent of the crude and had a softeningpoint of 441 F. as determined by the ring and ball test method. Thepenetration of the pitch as determined by ASTM test D5-49 at 210 F./ 100grams/ 5 seconds was 2. The pitch contained 0.11 percent materialinsolubles in trichloroethylene and had a Conradson carbon residue of55.2%.

Example 4 An Eastern Venezuela crude oil having a gravity of 33.2 APIwas distilled in an atmospheric distillation tower to yield 46.8 percentbottoms. The bottoms were then vacuum distilled at a flash temperatureof 788 F., an absolute pressure of 8.6 mm. of mercury and a steamaddition rate of 22.3 pounds per barrel of charge. The flashtemperature, corrected to 760 mm. of mercury, was

5 1138 F. The pitch recovered as bottoms from the vacuum distillationhad a specific gravity, in the solid state, of 1.124, a ring and ballsoftening point of 426 F., a Conradson carbon residue of 53.7 percentand contained 0.13 percent material insoluble in trichloroethylene.

Example 5 An Eastern Venezuela tar oil having a gravity of 14.8 API wasdistilled in an atmospheric distillation tower to yield 98.0 percentbottoms. The bottoms were then flashed in a vacuum distillation tower ata ash temperature of 761 F., absolute pressure of 6.6 mm. of mercury anda steam addition rate of 36.8 pounds per barrel of charge. The flashtemperature corrected to 760 mm. of mercury was 1170. The pitchrecovered as bottoms from the vacuum distillation had a specific gravityof 1.123, a ring and ball softening point of 369 F., a penetration at 77F., 100 grams, in 5 seconds of 1. The Conradson carbon residue was 46.4percent and the pitch contained 0.25 percent material insoluble intriclrloroethylene.

Example 6 A mixture of Western Venezuela crudes having a gravity of 12.5API was distilled in an atmospheric distillation tower to yield 96percent bottoms. The bottoms were then vacuum distilled at a ashtemperature of 785 F., a pressure of 8.7 mm. of mercury absolute andsteam added at the rate of 31.7 pounds per barrel of charge. The ashtemperature of the vacuum distillation corrected to 760 mm. of mercurywas 1180 F. The petroleum pitch recovered as bottoms had a specificgravity of 1.118, a lsoftening point of 356 F. and a penetration of at77 F., 100 grams and 5 seconds. The Conradson carbon residue was 46.7percent and the pitch contained 0.24 percent material insoluble intrichloroethylene.

Example 7 A Mara tar oil having a gravity of 15.0 API was distilled inan atmospheric distillation tower to yield 81.8 percent bottoms. Thebottoms were vacuum distilled at a ash temperature of 776 F., a pressureof 9.6 mm. of mercury absolute and a steam addition rate of 33.0 poundsper barrel of charge. The flash temperature corrected to 760 mm. ofmercury was 1170. The petroleum pitch recovered as bottoms from thevacuum distillation had a ring and ball softening poiht od 388 and aspecilc gravity of 1.139. The penetration of the pitch at 77 F., 100grams and seconds was 1. The Conradson carbon residue of the pitch was43.7 percent and the pitch contained 0.51 percent material insoluble intrichloroethylene.

We claim:

1. A process for the preparation of a petroleum pitch having a softeningpoint above about 350 F. and substantially complete solubility inbenzene consisting essentially of distilling in an atmosphericdistillation a petroleum crude oil selected from the group consisting ofnaphthenic base crude oils, asphaltic base crude oils and mixturesthereof, said petroleum crude oils having at least 30 percentasphaltenes in the residue from a ilash distillation at a temperature of1030 F., corrected to 760 millimeters of mercury absolute pressure,fofthe furnace oilfree bottoms of the crude oil, heating the bottoms fromthe atmospheric distillation under conditions of temperature andresidence time substantially to avoid cracking of the bottoms, addingsteam to the heated bottoms, and vacuum distilling the mixture ofbottoms and steam at an actual temperature in the range of 700 to 800F., the actual temperature and the amount of steam and the absolutepressure in the vacuum distillation being correlated to provide a flashtemperature of 1050 F. to about 1200 F., corrected to 760 millimeters ofmercury absolute pressure, to form the pitch as a residual product ofthe vacuum distillation.

2. A process for the preparation of a solid petroleum pitch having aring and ball softening point above about 350 F. and characterized bysubstantially complete solubility in benzene consisting essentially ofcontinuously vacuum distilling virgin bottoms of a crude oil having atleast 30% asphaltenes in the residue from a flash distillation at atemperature of 1030" F., corrected to 760 mm. of mercury absolutepressure, of the furnace oil-free bottoms of the crude oil, injectingsteam into the vacuum distillation, the actual ash temperature being inthe range of about 700 to 800 F. and correlated with the absolutepressure and the rate of steam addition to provide a distillationtemperature, corrected to 760 mm. of mercury absolute pressure, in therange of 1050 F. to about 1200 F., the rate of heating to the ashtemperature being such as substantially to avoid cracking of the virginbottoms, and cooling the residual product from the vacuum distillationvto produce a solid pitch.

References Cited in the tile of this patent UNITED STATES PATENTS1,615,407 Rogers et al Ian. 25, 1927 2,175,817 Slawson Oct. 10, 19392,305,440 Noel Dec. 15, 1942 2,366,657 Sorem Jan. 2, 1945 2,651,601 Taffet al. Sept. 8, 1953 2,662,051 Pelzer Dec. 8, 1953 2,717,866 Doering etal Sept. 13, 1955

1. A PROCESS FOR THE PREPARATION OF A PETROLEUM PITCH HAVING A SOFTENINGPOINT ABOVE 350*F. AND SUB STANTIALLY COMPLETE SOLUBILITY IN BENZENECONSISTING ESSENTIALLY OF DISTILLING IN AN ATMOSPHERIC DISTILLATION APETROLEUM CRUDE OIL SELECTED FROM THE GROUP CONSISTING OF NAPHTHENICBASE CRUDE OILS ASPHALTIC BASE CRUDE OILS AND MIXTUTES THEREOF, SAIDPETOLUM CRUDE OILS HAVING AT LEAST 30 PERCENT ASPHALTENESS IN THERESIDUE FROM FLASH DISTILLATION AT A TEMPERATURE OF 1030*F., CORRESTEDTO 760 MILLIMETERS OF MERCURY ABSOLUTE PRESSURE, OF THE FURNACE OILFREEBOTTOMS OF THE CRUDE OIL, HEATING THE BOTTOMS FROM THE ATMOSPHERICDISTILLATION UNDER CONDITIONS OF TEMPERATURE AND RESIDENCE TIMESUBSTANTIALLY TO AVOID CRACKING OF THE BOTTOMS, ADDING STEAM TO THEHEATED BOTTOMS, AND VACUUM DISTILLING THE MIXTURE OF THE BOTTOMS ANDSTEAM AT AN ACTUAL TEMPERATURE IN THE RANGE OF 700* TO 800*F., THEACTUAL TEMPERATURE AND THE AMOUNT OF STEAM AND THE ANSOLUTE PRESSURE INTHE VACUUM DISTILLATION BEING CORRELATED TO PROVIDE A FLASH TEMPERATUREOF 1050*F. TO ABOUT 1200*F., CORRECTED TO 760 MILLIMETERS OF MERCURYABSOLUTE PRESSURE, TO FORM THE PITCH AS A RESIDUAL PRODUCT OF THE VACUUMDISTILLATION.